void Swap(STUDENT * s1,STUDENT * s2){
    STUDENT tmp = *s1;
    s1->total = s2->total;
    s1->ce = s2->ce;
    s1->ws = s2->ws;
    for(int i=0;i<16;i++){
        s1->id[i]=s2->id[i];
    }
    s2->total = tmp.total;
    s2->ce = tmp.ce;
    s2->ws = tmp.ws;
    for(int i=0;i<16;i++){
        s2->id[i]=tmp.id[i];
    }
}